1. Field of the Invention
The present invention relates to a plasma display panel and a manufacturing method thereof, and more particularly, to electrodes in a plasma display panel which can reduce the cost of a material used for electrodes and prevent short circuiting between the electrodes, and a manufacturing method thereof.
2. Description of the Related Art
A typical plasma display panel is filled with a gas which is sealed inside the panel between two substrates where a plurality of electrodes are coated. When a discharge voltage is applied, ultraviolet rays are emitted due to the discharge voltage so that fluorescent substance formed in a predetermined pattern is excited to form numbers, characters, or graphics.
Plasma display panels can be classified as a DC (direct current) type or an AC (alternating current) type according to the type of a driving voltage applied to a discharge cell. Also, plasma display panels can be classified as a facing electrode type or a surface discharge type according to the configuration of electrodes. The DC type plasma display panel has electrodes which are all exposed to a discharge space, in which charged particles directly move between the corresponding electrodes. In the AC type plasma display panel, at least one electrode is enclosed by a dielectric layer, and a discharge is produced by an electric field of wall charges instead of charged particles directly moving between the corresponding electrodes.
FIGS. 1 and 2 show the structure of a typical AC type plasma display panel. Referring to the drawings, in a typical plasma display panel, a plurality of electrodes 11 are formed in a predetermined pattern on the upper surface of a rear substrate 10. A dielectric layer 12 is formed on the rear substrate 10 where the first electrodes 11 are formed. Barrier ribs 13 for maintaining a discharge distance and preventing cross talk between discharge cells is formed on the upper surface of the dielectric layer 12. A plurality of second electrodes 14 and a plurality of third electrodes 15 are formed on the lower surface of a front substrate 16 in predetermined patterns to cross the first electrodes 11. The front substrate 16 is coupled to the rear substrate 10 where the barrier ribs 13 are located. The second and third electrodes 14 and 15 are transparent electrodes and a plurality of bus electrodes 17 for reducing line resistance of the second and third electrodes 14 and 15 are formed on the lower surface of each of the second and third electrodes 14 and 15, such that each of the bus electrodes 17 has a width narrower than that of each of the transparent electrodes. A dielectric layer 19 is formed on the lower surface of the front substrate 16 where electrodes 14, 15, and 17 are formed. A fluorescent layer 18 is formed at at least one surface of discharge spaces defined by the barrier ribs 13.
In the plasma display panel, the bus electrodes 17 are of metal to reduce the line resistance of the transparent second and third electrodes 14 and 15. Thus, in order to minimize blocking of light emitted from the fluorescent layer 18, the bus electrodes 17 are located at an edge of each of the second and third electrodes 14 and 15 to have a width as narrow as possible.
The bus electrodes 17 are formed using a printing method using a metal material for example, silver (Ag) paste, a photolithography method using a photosensitive film, or a vapor deposition method.
The printing method is most advantageous in that the paste is cheap and the amount of the paste needed is small, i.e., ⅓through xc2xcless than the other methods. However, the width of the electrode line is limited to 60 through 70 xcexcm, so that forming accurate lines is difficult.
In the vapor deposition method, compared to the photolithography, the cost for a material is low and forming accurate lines is possible. However, the defective rate in an etching process is high and a high initial investment is needed.
In the photolithography method, the cost for an electrode pastes is high, and since a pattern is formed with only selected portions through an exposing process after printing the overall surface, the material is wasted. However, once a production line is set, the photolithography method is a very stable process and forming accurate electrode lines is possible.
FIGS. 3A through 3E show a method of forming the bus electrodes on the transparent electrodes using the photolithography method. Electrode paste 170 is applied to the overall surface of a glass substrate 16 where transparent electrodes 14 and 15 are formed by spin coating (FIG. 3A). Photoresist 22 is applied to the electrode paste 10 (FIG. 3B). A photomask 23 is placed on the photoresist 22 and the upper portion of the photoresist 22 is exposed to light (FIG. 3C). Then, the exposed electrode paste 17 is developed and baked so that bus electrodes 17 are completed (FIGS. 3D and 3E).
Here, an edge curl phenomenon in which portion of an electrode pattern is lifted is problematic in the photolithography method. FIG. 4 shows such an edge curl phenomenon, that is, both edges of one of the bus electrodes 17 are lifted. The lifting of the edge is known to be generated due to a difference in the compression rate between both edges and the middle portion of a bus electrode. The edge curl problem is described in a Japanese monthly magazine, xe2x80x9cFPD Intelligencexe2x80x9d, at page 45, May 1998 and page 60, November 1998. When the edge curl is generated, contact area between the bus electrodes and transparent electrodes is reduced so that contact resistance increases. Also, the height of the bus electrode increases due to the lifting thereof so that a dielectric layer becomes thin.
In addition, another problem in the photolithography method is short circuit between the electrodes. The short circuit occurs between the electrodes during the exposing process by intrusion of impurities in the paste where electrodes are present. The short circuit may cause a defective panel, and also damage a circuit so that the plasma display panel cannot even be repaired.
To solve the above problems, it is an objective of the present invention to provide electrodes in a plasma display panel which can save the cost for a material for electrodes, and prevent short circuit between the electrodes and the edge curl phenomenon, and a manufacturing method thereof.
Accordingly, to achieve the above objective, there is provided a method of manufacturing electrodes in a plasma display panel, which comprises the steps of (A) forming a pattern for electrodes on a substrate to be wider than a desired pattern, (B) coating photoresist on the electrode pattern, (C) disposing a photomask having the desired pattern on the photoresist and exposing the photoresist, and (D) forming electrodes having the desired pattern by developing and baking the exposed electrode pattern by using the photomask.
It is preferred in the present invention that the electrode pattern in step (A) is formed by a print method.
Also, it is preferred in the present invention that the electrode pattern is formed of silver (Ag).
Also, it is preferred in the present invention that the electrode pattern has a bulged middle portion and thin edge portions.
Also, to achieve the above objective, there is provided electrodes in a plasma display panel which are formed by forming a pattern of electrodes on a substrate to be wider than a desired pattern, coating photoresist on the electrode pattern, disposing a photomask having the desired pattern on the photoresist and exposing the photoresist, and forming electrodes having the desired pattern by developing and baking a pattern of electrodes exposed by the photomask.